Hello/New Double Blaster owner

[tibblits]

Hello everyone. Name's Stephen, I'm new to Blasters and 2 strokes in general. Traded my 2023 GPX MXR125cc pit bike and a .223 upper for these two blasters The green one was running good (so I thought) and the white one came with everything to get running I believe (the engine is out of it) but needs a bottom end rebuild, so I was told. I took the green one out shed hunting yesterday and when I was coming back in it started losing power quite noticeably and eventually died by the truck and I have not been able to start it since. It's getting spark and I checked the compression but it only put up about 35-40psi I'm guessing I fried the piston rings? I was 6th gear wide open for a bit right before this so maybe that has something to do with it but I would think you should be able to run these things however you want to without f*cking them up. I will say even tho it sounded like it ran really good it definitely didn't idle and there's no ignition hooked up with this one so it was just kick start and go lol and then it would die when you come to a stop. But it had tons of power and was an absolute blast so I'd like to get it running again but it sounds like from what I've been reading that maybe it wasn't tuned correctly because it should hold an idle. It never smoked or anything when it ran but I'd have to sit there and bump the throttle to keep it running if I was just sitting. Anyway I'm open to any and all suggestions you guys can give me as to why this happened because I don't want to rebuild it only for it to happen again. I don't know sh*t about 2 strokes but I'm semi mechanically inclined and don't have a budget for these things obviously I paid zero dollars for them lol but they are super sick so I'm willing to buy parts for them but not much else. Thanks y'all

 

[tibblits]

@RIDE-RED350r

 

[RIDE-RED350r]

Yeah, sounds like you have an air leak somewhere or a dirty carb that had you running lean. A property tuned and healthy 2-stroke should idle without a problem once up to temp.

When you dig into the topend, also fully disassemble and clean the carb. If it looks anything but clean and new inside, that will give you problems.

 

[tibblits]

Yeah, sounds like you have an air leak somewhere or a dirty carb that had you running lean. A property tuned and healthy 2-stroke should idle without a problem once up to temp.

When you dig into the topend, also fully disassemble and clean the carb. If it looks anything but clean and new inside, that will give you problems.

Sweet yeah it'll be a couple weeks before I can tear into it but I'm looking forward to becoming an expert on these things and get that white one up and running someday

 

[tibblits]

Ok so I was finally able to tear into the top end on the green party quad (yes that's what we call our quads around here ). Piston looks a little worn I'd say.

 

[RIDE-RED350r]

Yep, looks like a lean burn-down. Not normal wear and tear. Very likely that engine has an air leak somewhere.

 

[tibblits]

Yep, looks like a lean burn-down. Not normal wear and tear. Very likely that engine has an air leak somewhere.

Thanks.. that's what I figured. It's weird to me though because nothing seems out of the ordinary like all the gaskets looked good so not sure where the leak is coming from.

 

[RIDE-RED350r]

Crank seals, carb boot (dry rotted, cracked or just loose) cylinder base gasket and reed valve gaskets are the most common causes. Other less common cause could be a crack in the crankcase between the crankcase and transmission or other outside source of unregulated air can be taken in. But that's not very common. If all the top end gaskets appeared to be in good working order, crank seals would be my #1 suspect. But now that the top end is off you can't do a leak down test to verify/diagnose.

I'd figure on a full bottom-up rebuild myself. I had Ken O'Connor Racing rebuild the crank in my daughters Blaster over the winter. He did a great job, fast turnaround and very reasonably priced. I would highly recommend him if you choose to have the crankshaft rebuilt.

 

[tibblits]

Crank seals, carb boot (dry rotted, cracked or just loose) cylinder base gasket and reed valve gaskets are the most common causes. Other less common cause could be a crack in the crankcase between the crankcase and transmission or other outside source of unregulated air can be taken in. But that's not very common. If all the top end gaskets appeared to be in good working order, crank seals would be my #1 suspect. But now that the top end is off you can't do a leak down test to verify/diagnose.

I'd figure on a full bottom-up rebuild myself. I had Ken O'Connor Racing rebuild the crank in my daughters Blaster over the winter. He did a great job, fast turnaround and very reasonably priced. I would highly recommend him if you choose to have the crankshaft rebuilt.

How about if the port on the carb that used to be the oil supply was just a cut off hose would that be some of my problem? Just wondering.. I capped it anyways once I realized that's how it's supposed to be.

 

[RIDE-RED350r]

Yes, that would also be a source of unregulated air getting into the engine .

They could very well be your issue.

 

[RIDE-RED350r]

Have you ever replaced a top end in the past?? Particularly a 2-stroke??

 

[tibblits]

Have you ever replaced a top end in the past?? Particularly a 2-stroke??

I've never rebuilt a motor. Yesterday was a success though she fired right up and I watched Ken's break in procedure video before hand. Going to pick up an infrared thermometer today and do the next two heat cycles. She still doesn't idle but the ignition is bypassed somehow like there's no key cylinder or anything you just kick her over so maybe that has something to do with it idk.

 

[tibblits]

@RIDE-RED350r any idea why this thing "pees" after running it or if it's just sitting it lets out some fuel..? I figured out if I just turn the fuel off it doesn't piss on my concrete but just curious why it does this.

 

[RIDE-RED350r]

@RIDE-RED350r any idea why this thing "pees" after running it or if it's just sitting it lets out some fuel..? I figured out if I just turn the fuel off it doesn't piss on my concrete but just curious why it does this.

Fuel leaking from the carb overflow vent is one of three possible causes. Sticking float, fuel inlet needle and seat leaking/in need of replacement, or misadjusted float height. You have too much fuel in the bowl, this can also cause issues with fuel mixture across the board, including your issue with it not wanting to idle reliably.

 

[tibblits]

Fuel leaking from the carb overflow vent is one of three possible causes. Sticking float, fuel inlet needle and seat leaking/in need of replacement, or misadjusted float height. You have too much fuel in the bowl, this can also cause issues with fuel mixture across the board, including your issue with it not wanting to idle reliably.

Interesting. I messed with the idle screw a bit I turned it all the way in then backed it out 2.5 turns and she seems to idle there. Was running great until the fuel petcock on the carb just decided to pop off with the fuel hose and starting pissing out all over the road haha but I think I fixed it for now. Side note, how do I know if this thing has the right jets?

 

[RIDE-RED350r]

If you remove the jets, which will be readily accessible when you open up the carb to address the float/fuel inlet valve issue, you should find little numbers stamped on them.


The reason I asked if you had rebuilt a top end before is I wanted to give you a heads up about the piston ring locating pins in the ring lands of the piston. These ensure the ring gaps stay put and don't rotate out of place and end up snagging a port. Sounds like you got it sorted out as you would have a hell of a time getting the piston in the bore if the ring gaps weren't indexed to the locator pins properly.

 

[tibblits]

If you remove the jets, which will be readily accessible when you open up the carb to address the float/fuel inlet valve issue, you should find little numbers stamped on them.


The reason I asked if you had rebuilt a top end before is I wanted to give you a heads up about the piston ring locating pins in the ring lands of the piston. These ensure the ring gaps stay put and don't rotate out of place and end up snagging a port. Sounds like you got it sorted out as you would have a hell of a time getting the piston in the bore if the ring gaps weren't indexed to the locator pins properly.

Ok I didn't dive into the carb yet because I just wanted to get the sucker running again which it is but hopefully it's jetted correctly for my 5200' elevation and the giant pro circuit pipe on it.

It's interesting you mention that because the video that I watched on top end rebuild (rocky mountain atv) specifically said make sure you check your ring gaps and sure enough one of the rings was too tight so I dremeled it out just a hair until it was in spec. Even had my wife place the cylinder over the piston while I compressed the rings haha and tried my best to keep them lined up with those pins. It took some effort but mostly to get the rings compressed to where the cylinder could slide over them so hopefully they're where they need to be

 

[RIDE-RED350r]

So with higher elevation, you need less fuel. High elevation basic jetting changes usually begin at 5000'.. this is basic adjustments commonly listed in the owners/service manuals for the old 2-strokes like Blasters and 250Rs and whatnot. So with stock jetting, you will be a little rich at 5000' elevation. It's always best to start safely rich and incrementally work leaner one step at a time, one fuel circuit at a time, beginning with the main jet, then slide needle adjustment, then pilot jet/idle air screw. If you try to make more than one adjustment at a time, you will end up chasing your tail and pulling your hair out.

As to the ring gaps, good call to check that and adjust as necessary. The reason for specified ring gap is to allow the rings room to expand as they come up to temp without the ends crushing together, bulging out and scoring the cylinder or most commonly on a 2-stroke, snagging a port and ruining your day.

As to the ring indexing pins, if you got the piston into the cylinder, it's almost certain you got them placed properly. It would be at best extremely difficult to get the piston into the bore if the ring gaps weren't indexed on the pins. Obviously nothing is 100%, I suppose if the cylinder was extremely worn over spec you might be able to squeeze it in, but still not likely.

Good work!

 

[tibblits]

So with higher elevation, you need less fuel. High elevation basic jetting changes usually begin at 5000'.. this is basic adjustments commonly listed in the owners/service manuals for the old 2-strokes like Blasters and 250Rs and whatnot. So with stock jetting, you will be a little rich at 5000' elevation. It's always best to start safely rich and incrementally work leaner one step at a time, one fuel circuit at a time, beginning with the main jet, then slide needle adjustment, then pilot jet/idle air screw. If you try to make more than one adjustment at a time, you will end up chasing your tail and pulling your hair out.

As to the ring gaps, good call to check that and adjust as necessary. The reason for specified ring gap is to allow the rings room to expand as they come up to temp without the ends crushing together, bulging out and scoring the cylinder or most commonly on a 2-stroke, snagging a port and ruining your day.

As to the ring indexing pins, if you got the piston into the cylinder, it's almost certain you got them placed properly. It would be at best extremely difficult to get the piston into the bore if the ring gaps weren't indexed on the pins. Obviously nothing is 100%, I suppose if the cylinder was extremely worn over spec you might be able to squeeze it in, but still not likely.

Good work!

Nice. It was a new cylinder and piston so we should be good there. My main concern now is that I feel like it runs too hot.. I bought a infrared thermometer for the break in cycle according to Ken and I just got back from a ride and decided to shoot the temp again just for fun and she's sitting about 336°. That seems a little bit much to me but I rode it for probably 20 minutes so idk if that's normal or not. And as for the idle I thought we were good but I might have to back that screw out some more or go thru the entire carb like you mentioned.

 

[RIDE-RED350r]

Air cooled engines are a little tricky to get a good read on temp. I haven't seen the vid, but I'm guessing Ken suggests a specific area of the cylinder head when checking temp with an IR gun?

Remember, when adjusting the idle mixture screw, you are adjusting how much air is going to the idle circuit. So if you turn the screw clockwise you are reducing air thus enriching the idle mixture, and vice versa. This is not to be confused with the idle speed screw which is a screw that adjusts the position where the throttle slide rests when you are not touching the throttle lever. Set mixture first, then set idle speed.